By firing atoms of metal at another metal, Russian and American scientists reported Monday, they created a new element — No. 118 on the periodic table — that is the heaviest substance known.

Ununoctium, as the new element is temporarily named, has no known use but inspired almost a decade-long pursuit by scientists on four continents. Controversy in the course of its discovery hobbled the career of one physicist and almost wrecked the world’s most productive team of element hunters at Berkeley.

So far, science has gotten a fair measure of trouble out of element 118 for a substance that breaks down in a few thousandths of a second. As quickly as the discovery was announced, at least one competing team voiced doubts that it had been found at all.